Lighting arrester



Sept. 18, 1956 E, R w BECK A LIGHTNING ARRESTER Filed Oct. 14, 1954Fig.2.

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l l I wnmzsszs: B mvemoas Edward F.W. Beck 77 cndA|er1M.Opsohl BY q i IATTOR EY United States Patent LIGHTNING ARRESTER Beck, Pittsburgh, andAlert M. Opsahl, Pa., assignors to Westinghouse Electric EastPittsburgh, Pa., a corporation of Edward F. W. Forest Hills,Corporation, Pennsylvania The present invention relates to lightningarresters or overvoltage protective devices, and more particularly to anew type of lightning arrester utilizing semiconductor rectifierdevices.

Lightning arresters are used for protection of electrical equipmentagainst excessive voltage surges, such as lightning surges, and areusually connected between a line or a terminal of the protected deviceand ground. The arrester must be substantially a non-conductor undernormal conditions, but when a voltage in excess of a predetermined valueoccurs, it must become conducting substantially instantaneously todischarge the surge. The voltage across the arrester itself during thedischarge must not rise sufiiciently to endanger the protected device,and after the surge has passed and the voltage has fallen to or near itsnormal value, the arrester must again become non-conducting and mustinterrupt the power current which tends to flow through the arrester dueto the normal line voltage.

In conventional lightning arresters of the valve type, theserequirements are met by the use of a valve element, or non-linearresistor, connected in series with a spark gap. The spark gap normallyisolates the valve element from the line but sparks over at apredetermined voltage and allows surge current to flow to ground throughthe valve element, which has low resistance and thus a low dischargevoltage under high current conditions. When the surge has beendischarged, the valve element increases its resistance and reduces thepower current to a small value which is readily interrupted by the sparkgap. The valve elements usually used consist of granular silicon carbidewith a binder of sodium silicate or other suitable material, andfrequently with other constituents such as clay. The heterogeneousnature of this mixture and the difficulty of obtaining uniformity of thevarious constituents, especially of the silicon carbide, have made itvery ditficult to control the characteristics of these valve elements inmanufacture, and the variability of the valve elements is a seriousproblem in conventional lightning arresters.

The principal object of the present invention is to provide a new typeof lightning arrester in which the conventional valve elements areeliminated, and in which uniform and readily controllablecharacteristics are obtained.

Another object of the invention is to provide a lightning arrester inwhich semiconductor rectifier devices are utilized for discharging surgevoltages with low voltage during the discharge, and for substantiallyinterrupting the power current at the first current zero following adischarge.

Other objects and advantages of the invention will be apparent from thefollowing detailed description, taken in connection with theaccompanying drawing, in which:

Fig. 1 is a schematic diagram illustrating the invention; and

Figs. 2 and 3 are somewhat diagrammatic views, partly in section,showing illustrative embodiments of the invention.

The lightning arrester of the present invention is shown schematicallyin Fig. 1. As there shown, the new arrester consists of twoparallel-connected groups of elements. Each of these groups consists ofa plurality of rectifier devices 1 connected in series, and a spark gapdevice 2 connected in series with the rectifier elements. The rectifiersare preferably semiconductor rectifier devices of the p-n junction type,such as silicon or germanium rectifiers. Rectifiers of this type arecapable of carrying relatively large currents in the forward orconducting direction, with low voltage drop across the rectifier in theforward direction. These devices are also capable of withstandingrelatively high voltages in the reverse direction with extremely lowleakage currents.

The rectifier devices 1 of each of the two groups are connected inseries with a spark gap 2 and the two groups are connected in parallelwith the rectifiers of the two groups connected in opposite directions,that is, the forward or readily conducting direction of one group isopposite to that of the other group. The spark gap devices 2 may beconnected together as indicated at 3, and connected to a line or otherprotected device 4, and the op pcsite ends of the two series groups ofrectifiers are connected together at 5 for connection to ground. Anysuitable number of rectifier devices may be used in series, dependin onthe voltage rating desired, and each of the parallel-connected groupstherefore consists of one or more rectifier devices in series with aspark gap device.

in the use of this device, it is usually connected between line andground, as shown. Under normal conditions, the spark gap devices 2isolate the rectifiers 1 from the line so that the device is anon-conductor. Upon the occurrence of a voltage surge on the line 4 inexcess of a predetermined magnitude, such as a lightning surge, one orthe other of the spark gaps 2 will break down and become conducting. Itwill be understood that such voltage surges may be of either polarity,and will be in the forward direction of one or the other of the twoparallel groups of rectifiers, If the magnitude of the surge exceeds thebreakdown voltage of the gaps 2, the gap of the group of rectifierswhich is in the forward direction for the polarity of the surge will areover, and permit the surge to be discharged to ground through therectifiers. The other group of rectifiers is in the reverse directionfor the polarity of the surge, so that it presents a very high impedanceand the associated gap 2 will not break down. The surge is discharged,therefore, through one or the other of the two groups of rectifiers, andthe voltage across the arrester during the surge is only the sum of therelatively low forward drops of the rectifiers 1. The discharge voltageof the arrester therefore is quite low.

After the surge has been discharged, power current will continue to flowthrough the rectifiers 1 to ground until the next current zero of theline current, when the current passes through zero and reverses inpolarity. The group of rectifiers through which the current has beenflowing is then in the reverse direction with respect to the polarity ofthe current, and only an extremely small leakage current can flowthrough the rectifiers in the reverse direction. This current is sosmall that it cannot maintain a stable arc in the gap 2, and the currentis easily interrupted by the gap. The other parallel group of rectifiersis, of course, in the forward direction of the current after the currentzero, but since the gap of that group had not arced over, no currentwill flow. Thus, the arrester reliably interrupts the power current andagain becomes a non-conductor at the first current zero following adischarge.

Fig, 2 shows somewhat diagrammatically a practical embodiment of theinvention. In this embodiment, the two groups of rectifiers arecontained in cylindrical housings 10 of porcelain, or other suitableweather-proof insulating material. Each of the housings contains a stackof semi-conductor rectifier devices 11 disposed in the housing in seriesrelation, the rectifier stacks of the two housings being arranged withtheir forward directions opposite to each other, as explained above inconnection with Fig. 1. The housings are closed at the top and bottom bymetal fittings or caps 12 and 13 which may be secured to the housing inany suitable manner, as by cementing. The bottom caps 13 of the twohousings may be secured to a metal mounting plate 14 which electricallyconnects the two groups of rectifier devices and which may be providedwith a terminal device 15 for connection of a ground lead. Therectifiers 11 are preferably held in good electrical contact with eachother and with the end caps by spring means indicated diagrammaticallyat 16. An electrode member 17 of any suitable type is mounted on theupper cap 12 of each housing in electrical contact therewith. A commonelectrode 18 is disposed between the two electrodes 17, to form separatespark gaps with them, and is provided with a terminal device 19 forconnection of a line lead. The common electrode 18 may be supported inany suitable manner, and is shown as being mounted on an insulator 20placed on top of one of the housings in. It will be evident that thisarrester is identical electrically to the diagram of Fig. l, and itsoperation is as described above.

Fig, 3 shows another embodiment of the invention which may be utilizedwhere open spark gaps may be undesirable. In this embodiment, therectifier devices 11 are disposed in porcelain housings 10, as before,and spark gap devices 21, preferably consisting of a plurality ofindividual gaps 22 of any suitable construction, are placed within thehousings 10 in series relation with the rectifiers 11. The housings 10are mounted as described above in connection with Fig. 2, and aconducting plate or member 23 is secured on the upper caps 12 toelectrically connect them together and may be provided with terminalmeans 24 of any suitable type for connection of a line lead. It will beseen that the operation of this arrester is the same as that previouslydescribed.

It will now be apparent that a new type of lightning arrester has beenprovided which completely eliminates the use of conventional valveelements, and therefore avoids the difficulties of non-uniformity andvariable characteristics which have been serious problems inconventional arresters. The new arrester utilizes semiconductorrectifier devices which have very uniform characteristics which arereadily controllable in manufacture, and thus accurately predeterminedperformance is obtainable. The characteristics of semiconductorrectifiers are very suitable for lightning arresters since they candischarge heavy surge currents with low voltage drop, and have very lowreverse leakage current, so that the power current can easily beinterrupted.

Certain specific embodiments of the invention have been shown anddescribed for the purpose of illustration, but

4 it will be understood that various other embodiments and modificationsare possible and are within the scope of the invention.

We claim as our invention:

1. A lightning arrester comprising two groups of elements connected inparallel, each of said groups consisting of at least one semiconductorrectifier device and a spark gap device connected in series, therectifier devices of the two groups being connected in oppositedirections.

2. A lightning arrester comprising two groups of elements connected inparallel, each of said groups consisting of a plurality of semiconductorrectifier devices and a spark gap device connected in series, therectifier devices of the two groups being connected in oppositedirections.

3. A lightning arrester comprising a first group of seriesrelatedsemiconductor rectifier devices, a spark gap device connected in serieswith said rectifier devices, a second group of series-relatedsemiconductor rectifier devices, a second spark gap device connected inseries with said second group of rectifier devices, means for connectingthe two spark gap devices to a common terminal means, and means forconnecting together the ends of the two groups of rectifier devicesopposite to the spark gap devices, the rectifier devices of the twogroups being disposed with their conductive directions opposite to eachother.

4. A lightning arrester comprising a pair of insulating housings, aplurality of series-related semi-conductor rectifier devices in each ofsaid housings, a spark gap device in each housing in series relationwith the rectifier devices, means for connecting the spark gap devicesof both housings to a common terminal means, and means for connectingtogether the other ends of the two series of rectifier devices, therectifier devices of the two housings being disposed with theirconductive directions opposite to each other.

5. A lightning arrester comprising a pair of insulating housings, aplurality of series-related semi-conductor rectitier devices in each ofsaid housings, means for connecting one end of the series of rectifierdevices in one housing to one end of the series of rectifier devices inthe other housing, the rectifier devices of the two housings beingdisposed with their conductive directions opposite to each other, anelectrode member supported on each housing and connected to the otherend of the series of rectifier devices therein, and a common electrodemember supported between said first-mentioned electrode members andforming spark gaps therewith.

UNITED STATES PATENTS References Cited in the file of this patent1,345,066 Brackett June 29, 1920 1,745,690 Pritchett Feb. 4, 1930FOREIGN PATENTS 551,443 Great Britain Feb. 23, 1943 667,846 GreatBritain Mar. 5, 1952

